The present invention is generally directed to a high-speed and high-density cable connector which is specifically designed for direct connection to a corresponding connector adjacent to a semiconductor chip site on a printed circuit board. Even more particularly, the present invention is directed to a cable connector which employs only a single intermediate element between cabling entering the connector assembly and an edge wafer connector which is designed, positioned and constructed to make contact with a standard printed circuit board connector.
In the design of a simulation engine for large mainframe computer systems, it became clear that some means would have to be provided to make connections directly to connectors which are adjacent to semiconductor chip elements arrayed on a printed circuit board. The simulation engine which was constructed is an exceedingly flexible device capable of a very wide range of emulation functions. However, as is well known, an emulator cannot produce the same real-time operation as the ultimate hardware system which it is designed to emulate. Clearly therefore, it is very important for emulation machines to be run at very high speed. It should be appreciated, therefore, that the speed considerations for emulation machines are, in fact, more rigorous than speed requirements for the end pieces of computer hardware which they are designed to emulate for the purposes of debugging the design. Accordingly, it was determined that cable connections had to be made directly to printed circuit boards at locations immediately adjacent to semiconductor chip sites. However, conventional ribbon cable and connectors are inadequate for this task because of the high-speed requirements (greater than 100 MHz). Accordingly, it became necessary to design a particular connector assembly system which is useful in an emulation machine and, in particular, which is capable of providing direct connections to a printed circuit board at a location adjacent to a chip site. This is in sharp distinction to board edge connectors which do not necessarily have the same rigorous timing constraints in terms of their speed or frequency rating. This is because the connectors of the present invention are meant to connect on the chip-to-chip level rather than the board-to-board level where speed and distance constraints are much less severe.
In the construction of a desired connector assembly, a number of important criteria had to be met. In particular, it was very desirable that cable handling and routing did not significantly alter the electrical characteristics of the cable or the connection. It was important for the connector and for the cabling design that variations in measured impedance were in the range of approximately 10 milliohms. In the design of connector and cabling assemblies, it is also noted that each and every intermediate connection between the cable and the connector is a potential point of degradation. This potential degradation path is further enhanced by the fact that the specific requirements for the emulation system for which a cable design was needed meant that the linear density of connections in terms of lines per inch was quite high. In particular, there was a requirement for 38 signal lines to be accessed at each semiconductor chip edge which was only 32 mm wide. Additionally, the system requirements, which were primarily dictated by the size of the semiconductor chips themselves, meant that the spacing between adjacent signal lines was only 0.025 inches. Thus, the emulation system in question produced extremely tight requirements for cable and connector speed and, concomitantly, severe requirements for signal line spacing.
Small spacing between signal lines produces significant problems in the design of high-speed cabling systems. In particular, the present inventor has appreciated the fact that connection of cable wiring within the connector assembly precludes the utilization of flux-based solders. In particular, it is noted that the spacing requirements are so stringent that the tendency of flux-based solder attachment methods unfortunately results in contamination of the cable dielectric and, furthermore, results in the growth of dendritic material. While dendrite growth is tolerable in certain applications, when the spacing between signal and/or ground conductors is tight, the dendritic growth problem becomes severe. Accordingly, it was necessary to devise a connector and connector assembly approach which simultaneously eliminated all of these problems.